Shuzo Kawarazaki

Effects of pressure on tiny antiferromagnetic moments in the heavy-electron compound URu2Si2

We have performed elastic neutron-scattering experiments on the heavy-electron compound URu_2Si_2 for pressure P up to 2.8 GPa. We have found that the antiferrmagnetic (100) Bragg reflection below T_m ~ 17.5 K is strongly enhanced by applying pressure. For P < 1.1 GPa, the staggered moment mu_o at 1.4 K increases linearly from ~ 0.017(3) mu_B to ~ 0.25(2) mu_B, while T_m increases slightly at a rate ~ 1 K/GPa, roughly following the transition temperature T_o determined from macroscopic anomalies. We have also observed a sharp phase transition at P_c ~ 1.5 GPa, above which a 3D-Ising type of antiferromagnetic phase (mu_o ~ 0.4 mu_B) appears with a slightly reduced lattice constant.

Magnetic properties of U(Ru1−xRhx)2Si2 single crystals (0≤x≤1)

The temperature dependence of the nonlinear susceptibility of URu{sub 2}Si{sub 2} has been studied in order to understand the properties of the phase transition at 17.5 K. We have also studied the various magnetic phases of U(Ru{sub 1{minus}{ital x}}Rh{sub {ital x}}){sub 2}Si{sub 2} as a function of {ital x} by means of specific heat, susceptibility, and neutron scattering experiments. Special attention has been paid to {ital x}=0.3 where two successive phase transitions occur.The temperature dependence of the nonlinear susceptibility of URu2Si2 has been studied in order to understand the properties of the phase transition at 17.5 K. We have also studied the various magnetic phases of U(Ru1−xRhx)2Si2 as a function of x by means of specific heat, susceptibility, and neutron scattering experiments. Special attention has been paid to x=0.3 where two successive phase transitions occur.

Magnetic Properties of (Fe1-xCox)Si

The magnetic properties of (Fe 1- x Co x )Si have been studied by means of low temperature specific heat, Co 59 nuclear magnetic resonance and Mossbauer effect of Fe 57 . An Fe atom substituted for a Co atom in CoSi gives rise to a paramagnetic moment on six nearest neighbor Co atoms. All quantities measured suggest that the magnetic electrons are itinerant. The relationship between the magnetic electron and the transport electron is discussed.

Neutron diffraction study on the hyperfine-enhanced nuclear spin order of HoVO4☆

Abstract A neutron diffraction experiment on the hyperfine enhanced nuclear spin system of HoVO4 has been carried out following adiabatic demagnetization cooling. Below 4.5 mK we observed magnetic diffraction peaks due to antiferromagnetic order of the hyperfine enhanced nuclear spin system. A spin-flop transition in an applied magnetic field of about 80 Oe was also observed. The neutron diffraction results are consistent with the magnetic structural model proposed by Bleaney on the basis of dipolar energy considerations.

Neutron diffraction study on the magnetism of the Ce(Ru1−xRhx)2Si2 mixed compound system

Abstract We have studied the magnetic properties of the pseudo-binary system Ce(Ru 1- x Rh x ) 2 Si 2 by means of neutron diffraction with single crystalline samples. In the intermediate phase with 0.05 ⩽ x ⩽ 0.25, we observed incommensurable magnetic modulation. Since no higher order component was observed and the polarization is uniaxial (along the c -axis), the modulation is regarded as purely sinusoidal. The magnetic structure of CeRh 2 Si 2 is discussed on the basis of the exact atomic magnetic moments of Ce.

Long Range Magnetic Order on the Kondo Lattice. SDW in Ce(Ru1-xRhx)2Si2 as Studied by Neutron Diffraction.

We report results of neutron-diffraction experiments which have been carried out to study the long range magnetic order developing on the Kondo lattice of the pseudo-binary-alloy system Ce(Ru 1- x Rh x ) 2 Si 2 with x around 0.15. The ground-state structure of the ordered phase has a sinusoidal modulation of the moment, that is, a modulation with an incommensurable wave number and a uniaxial polarization. We assign this phase to the same category of magnetism as that of the spin-density wave in metals. Several characteristic quantities of this ordering such as the order parameter, the wave number, the amplitude and the anisotropy of the polarization and the anomaly in the lattice-constant are analyzed and discussed in terms of either the s-d model or the hybridized f-band model of Kondo effect.

Quantum critical point of an itinerant antiferromagnet in a heavy fermion

A quantum critical point of the heavy fermion Ce(Ru(1-x)Rh(x))2Si2, (x = 0,0.03) has been studied by single-crystalline neutron scattering. By accurately measuring the dynamical susceptibility at the antiferromagnetic wave vector k3 = 0.35c*, we have shown that the inverse energy width gamma(k3), i.e., the inverse correlation time, depends on temperature as gamma(k3) = c1 + c2T((3/2)+/-0.1), where c1 and c2 are x dependent constants, in a low temperature range. This critical exponent 3/2 +/- 0.1 proves that the quantum critical point is controlled by that of the itinerant antiferromagnet.

Structure of the Magnetic Modulation in the Coupled Electron-Nuclear Magnet PrCu2

Neutron diffraction experiments have been carried out at milliKelvin temperatures in order to study the magnetic structure of the coupled electron-nuclear system PrCu 2 . Polarization analysis and intensity analysis reveal that in the ordered state electronic and nuclear moments of the praseodimium atoms are sinusoidally modulated in magnitude and oriented approximately parallel to the crystal a -axis. The Jahn-Teller strain which induces a structural distortion at 7.3 K affects the magnetic domain structure, showing a coupling with the magnetic modulation. The temperature dependences of the diffraction intensity of several magnetic satellites indicate that PrCu 2 belongs to the nuclear regime where the leading part of the phase transition is the nuclear spins.

Spin fluctuation in heavy fermion CeRu2Si2

Spin fluctuations of the archetypal heavy fermion compound CeRu2Si2 have been investigated by neutron scattering in an entire irreducible Brillouin zone. The dynamical susceptibility is remarkably well described by the self-consistent renormalization (SCR) theory of the spin fluctuation in a phenomenological way, proving the effectiveness of the theory. The present analysis using the SCR phenomenology has allowed us to determine 14 exchange constants, which show the long-range nature of the Ruderman-Kittel-Kasuya-Yosida interaction.

Field-induced Ferromagnetic Correlation in the Metamagnetic Crossover in CeRu2Si2 as Studied by Neutron Scattering

Neutron inelastic scattering experiments have been performed on the paramagnetic heavy fermion compound CeRu 2 Si 2 in magnetic field along the crystal c -axis. Around the metamagnetic crossover field H m =7.7 T, the quasi-elastic excitation in the vicinity of the reciprocal lattice point (110) with an energy of 0.4 meV is significantly enhanced at T =0.4 K. The result indicates that the metamagnetic crossover in this compound is associated with a field-induced ferromagnetic correlation. The observation is consistent with the recent theoretical prediction by Satoh and Ohkawa based on quasi-particle band spectrum considerations.